Operating Systems: Design and Implementation (a.k.a the MINIX book). This is one of the books Linus Torvalds used to write the original Linux kernel. This also contains over 500 pages of the entire MINIX source code at the back as an appendix, and if you're lucky, a MINIX installation CD with instructions.

The Art of Computer Programming by Donald Knuth (essentially the holy grail of Computer Science literature). Bill Gates said that if anyone can read every volume in TAOCP from cover to cover, then they should definitely send him their CV/Resume.

The Pragmatic Programmer Cuts through the increasing specialization and technicalities of modern software development to examine the core process—what do you do, as an individual and as a team, if you want to create software that’s easy to work with and good for your users.

Introduction to Algorithms The book covers a broad range of algorithms in depth, yet makes their design and analysis accessible to all levels of readers.

The Tao of Programming The themes of the book espouse many hacker ideals – managers should leave programmers to their work; code should be small, elegant, and maintainable; corporate wisdom is more often than not an oxymoron; and so on.

Hacker's Delight It discusses a variety of programming algorithms for common tasks involving integer types, often with the aim of performing the minimum number of operations or replacing slow operations by faster ones.

Code Complete A compendium of software construction techniques, from naming variables to deciding when to write a subroutine.